Ok i need to replace my o2 sensors and i was just wondering how hard its going to be to get these out of the pipes. The truck has 110,000 miles on it and still has the original o2 sensors. Im getting a "system to lean code so im thinking there probably bad. Also i have a BAD!! exhaust leak right where the exhaust manifold connects to the catalytic converter, it looks like its just missing a gasket. The bolts that connect the two peices are stuck on there pretty good. How could i get those bolts off? Any ideas? right now it just has a pound of exhaust putty on the leak to get me through the winter.

99 v6 f150 4x4

 

I just had a po171 and po174 lean code check engine light and it wasnt the o2 sensors, it was the air intake manifold. Hopefully this isnt the same for you since its an 800 dollar job. I hear if it isnt the o2's in the front that the ones that control the back wont cause a lean code. Good luck in your findings

 

If the only codes you got are for system lean condition then there is about a 90% chance that there is an air leak downstream of the MAF sensor. Normally when an O2 sensor dies you will get a codes for O2 sensor responding slow, O2 trim over range or the PCM is not getting a signal from the O2 sensor.
It definitely is a good idea to change the O2 sensors out seeing how old they are but dont be surprised if the lean codes come back.

 

Have the cats checked. These things cause major problems when they are hooped. It might sound like an exhaust leak, but it might be a plugged cat forcing the exhaust back where you don't want it to go.

 

im definitely changing the sensors out when in warms up a bit. Are they gunna be a **tch to get out?

 

not usually. they have antiseize on them from the factory. they make a special tool for removing them, but a wrench works okay. whenever i replace one, i cut the harness off that goes into the sensor to make it easier to get an end wrench on it. you'll want to make sure you put antiseize on the sensor's threads if there isn't any on there from the factory.

 

Since the others who said this weren't clear enough, here it is in plain English: You are wasting your money on O2 sensors, they won't fix code 171 and 174. There are different codes for O2 sensor performance. If the O2 sensors don't work properly codes 171 and 174 can't be properly evaluated. If you want 171 and 174 fixed you have to either clean your MAF, fix a vacuum leak, or find out why your fuel supply isn't good enough.

 

IMO the shops that recommend replacing the O2 sensors on a every xx,xxx miles are either just trying to milk more money out of people, or they have know idea how to troubleshoot an obII engine control system. I am sure that the O2 sensors performance degrades as they get older but I have yet to witness an engine that got better gas mileage or more power from replacing an old O2 sensor that was not tripping a "lazy" or "missing" O2 sensor code. There is only 2 ways they can fail, the first is iff the wires to the sensor are broken/cut and the other is if the sensor gets dirty or coated with something that insulates it from the exhaust gasses.
From what I have read the likely culprit is the 90 degree elbow in the PCV hose behind the throttle body.

 

02 sensors do go bad, if not why does Bosch sell replacement parts?
I did read these should be replaced after 100,000 as a maintanence item.
I replaced all three on my 96 FSB and cleared all the codes but one. (I may have a damaged wire in the 02 system).
A bad EGR can also throw a lean code too.

I suggest looking for a leak in the system before intake.

I sprayed all my sensors with a penetrating oil about an hour before I started the work. It is not problem to get these off. My replacement sensors had antisieze on them from Bosch already.

With over 100,000 miles on the truck, you might as well replace everything you can.
Belts
Hoses
Filters
Coolant

 

I know this sounds far fetched, but maybe they want your money?

I don't think the statement was ever made that O2 sensors don't go bad, just that they won't cause codes 171 and 174. If the PCM doesn't see a problem with them there is very little chance that they are not performing as they should.

 

im a preventive maintenance freak so i was just thinking it might pick me up some more MPGs ive been reading ip on the p0174 code and i think i will go ahead and replace the upper intake manifold gasket maybe even lay a coat of red paint the manifold

 

I had codes 171 and 174 and new o2 sensors cleared the codes. I'm sorry to sound rude if but you don't know what you're talking about, don't speak with such conviction. To someone who truly doesn't know the way it should be, speaking the way you did your post can sound very convincing, whether it's right or wrong.

O2 sensors DO GO BAD!! Of course they do. They are constantly being heated and cooled every time you start and stop the truck, not to mention your sending exhaust fumes and god knows what else (burned oil smoke, burned coolant smoke, etc etc). There is NO WAY that you can say all o2 sensors are invincible. On a perfectly running truck with nothing but fuel and air being burned ALWAYS (nearly impossible), I'd imagine that they'd last an incredibly long time but the fact of the matter is, that's a highly implausible situation. My 95 runs like a top and my truck threw 171 and 174 at ~100k miles and replacing the o2 sensors cleared them.

 

Those 2 codes are 99% of the time for either a bad PCV elbow or a dirty MAF sensor.
Usually when the O2 sensors fail, it is the heater in them that burns out and there is a separate code for that. This is why they make replacement sensors.
There is also a code for a slow response from an O2 sensor.
lean codes are caused by something else, but you can waste your money replacing them. It will not help mileage except for your wallet will be lighter, so the truck will be hauling less weight around.


Chris, OBD-II that came out in 96 is a totally different animal then your old OBD-I/OBD-II set-up in your 95.

 

Your point holds water, but the facts don't lie. I'm only one of MANY guys on our 87-96 forum who have replaced their o2 sensors and realized better performance/fuel economy due to having malfunctioning sensors before. Of course there's no way for me to PROVE that new o2 sensors cleared my codes but what benefit do I get from lying here? Anyways, none of that really matters. I'm just saying that you cannot make such a general statement about all o2 sensors being invincible, the part goes bad sometimes, bottom line. If you want to claim that it's UNCOMMON for them to go bad, sure, that's a completely valid point.

And I do know what OBD-II is, it was used in the 96 F150s (my truck's era) and the 97 F250/350s (also my trucks era). The main difference between the two diagnostic systems is precisely that, the diagnostic system. The OBD-II doesn't change the way the truck operates (or the way the o2 sensors operate for that matter), it only involves changes in the way the truck MONITORS the way the engine and drivetrain are operating, and has a much larger and more specific code database. But the vehicle operation between the two diagnostic systems do not differ, assuming that your staying within one specific style of engine (be it pushrod or modular).

Anyways, if you guys wanna know if I'm 'lying' about the guys on my forum replacing their o2 sensors with MUCH success, just make a post over there and ask these same questions! Guaranteed many of the regulars will tell you the same thing I'm telling you now, o2 sensors are NOT invincible.

https://www.ford-trucks.com/forums/forum28

 

Wow! I didn't mean to stir the pot so much. I didn't mean for everyone to think that O2 sensors dont go bad I just dont think they go bad as often as repair shops tell everyone. I work in process controls so I spend most of my time troubleshooting control systems so I am fairly good at isolating faulty components and I do all of the preventative maintenance on about 35 different control systems and I have never worked on a system that had me replace a sensor as preventative maintenance, calibrate yes but not replace. Every time the engine is started the engine gets to operating temp the PCM tests the O2 sensors before it switches to closed loop operation, to me It does not make sense to replace the sensors unless they fail they start failing the self test.